In a conventional apparatus for descaling or cleaning the surface of a steel strip, a storage tank for storing abrasives is connected through a supply line to a nozzle so that abrasives are projected against the surface of a steel strip by either a jet of water or air under high pressure. The abrasive used in this manner are not recovered for reuse. Anticorrosion paint, or the like, is supplied from a storage tank through a jet pump to the nozzle to be projected over the surface of the strip steel. Furthermore, the anticorrosion paint is not collected for reuse.
The above-described conventional apparatus has the following drawbacks:
A. The abrasive supply line tends to be clogged often since the abrasives are supplied to the nozzle by a jet of compressed air or vacuum produced by the injection of water under high pressure. As a result of this arrangement, the descaling or cleaning efficiency is poor and automation is difficult.
B. Since the abrasives are transported by air, heavy and hard particles cannot be used.
C. Since the abrasives and anticorrosion paint are not recovered, the operational cost is very high.
D. When the abrasives are to be recovered, there must be provided a separator, a dryer and associated structure. Therefore, a large space is necessary and the installation cost becomes very expensive.
In the conventional abrasive blasting method in which the operators hold the nozzles and move along a steel strip to descale or clean, many work operations are required and the time required for polishing or cleaning is considerable. Furthermore, the quality of the finished surface is generally poor, especially when the surfaces of a workpiece with a complex structure are finished. Moreover, the time required for finishing each surface is not uniform, and the finished surfaces are not uniform even when finished by skilled workers. Thus, it is difficult to provide the desired uniformly finished surfaces for workpieces.
Furthermore in view of the government requirements regarding protection against health hazards, the conventional abrasive blasting methods are not preferable because when the dry method is used the abrasives are scattered indiscriminately and when the wet method is used, water droplets are scattered indiscriminately. The work efficiency is also considerably reduced.
One of the objects of the present invention is to provide a method and apparatus for abrasive blasting which may prevent the clogging of a supply line.
Another object of the present invention is to provide an abrasive blasting method and apparatus in which abrasive blasting pressure may be arbitrarily selected.
Another object of the present invention is to provide an abrasive blasting method and apparatus in which the used abrasives may be recovered.
A further object of the present invention is to provide an abrasive blasting method and apparatus which may descale or clean the surfaces of an object or work of complex shape in a uniform and efficient manner without causing any health hazards to the workers.